Various types of surfaces, such as stationary surfaces (on buildings and especially their windows), or such as mobile surfaces (on transport vessels, such as aircraft and ships), have periodic needs for cleaning, inspection, and other repair or maintenance operations. A wide variety of robotic devices have heretofore been used or proposed in various situations for performing a variety of working operations, such as cleaning or polishing surfaces, that are not easily accessible for manual conduct of such operations. In general though, the most successful prior art robotic devices have been used on flat or planer surfaces such as windows, building panels and the like. That is because such prior art devices typically operate with vacuum equipment that easily moves over smooth, continuous surfaces. However, various prior art robotic devices suffer from partial or complete vacuum loss which can result in detachment of the robot from the surface when they encounter uneven, discontinuous, or curved surfaces (and particular surfaces with multiple curvatures).
Unfortunately, in many applications for robotic devices, the presence of discontinuous or multiple curved surfaces are encountered. In one potential application, namely the inspection and maintenance of the surfaces of large commercial aircraft, such multiple curvature type surfaces are encountered at a variety of locations. Use of robots in such an application has heretofore been problematic, even though the potential is great. Instead of using robots, due to the large size and shape of such aircraft, it is currently customary to erect a scaffold alongside of the aircraft, and to employ a number of workers supported on the scaffold to hand scrub the aircraft surfaces. After scrubbing, the aircraft is waxed and polished using manual rotary buffers. Such buffers are relatively heavy, and due to the enormous surface area of large commercial aircraft, buffing operations are tedious and time consuming. For example, the entire operation of scrubbing, waxing and buffing a large commercial transport aircraft often takes a period of time in the 20 to 30 hour range, utilizing 10 or more workers.
In another related and important potential robotic application, commercial aircraft are subjected to a non-destructive inspection after a specified number of cycles of pressurization, for example about 7,000 cycles of pressurization for aircraft under regulation by the United States Federal Aviation Administration. Each take-off and landing in which the aircraft is pressurized is considered to be one pressurization cycle. In a typical non-destructive inspection, the paint is stripped entirely from the aircraft, and the seams and rivets are manually inspected. If a defect is observed during the inspection, the area of the defect is marked for further evaluation. Such suspect areas are then subjected to additional tests, such as an eddy-current sensor test, to determine the nature and magnitude of the defect. After further inspection and necessary repair, the aircraft is repainted, and is then waxed and buffed.
The normal paint stripping, inspecting, repainting, waxing, and buffing operation is extremely time-consuming and labor intensive, resulting in a substantial expenditure. Also, the paint stripping operation presents a potentially serious environmental problem, in that solvents are often used to remove the paint. Thus, pollution abatement equipment is then necessary in order to remove the solvent fumes from the paint stripping area.
In the various prior art robotic devices which have attempted to navigate the surfaces of aircraft, and particularly aircraft hulls, the presence of (a) gaps in the skins, which result in loss of vacuum in devices which depend on sequential vacuum locomotion, and/or (b) tight radius or compound curves, which confound various locomotion schemes, have resulted in the inability of such prior art devices to successfully navigate such surfaces. Accordingly it would be desirable to provide a robotic device that can easily traverse gaps in surfaces, and which can easily maneuver over curved surfaces, particularly curved surfaces with multiple radii or compound curved surfaces.
Similarly, in other applications such as buildings, when traversing discontinuities such as window frames, or sealant gaps between installed building panels, the presence of such discontinuities result in partial or complete loss of vacuum in many prior art devices. Likewise, it would be desirable to provide a robotic device that can easily traverse surface discontinuities and gaps.